1. Field of the Invention
The present invention relates to a fabrication aiding apparatus configured to aid the fabrication of a dental prosthesis such as an inlay, crown, bridge or a like.
2. Description of the Related Art
A conventionally known method for fabricating a dental prosthesis such as an inlay, crown, bridge, or a like includes a method of casting a metal material using a so-called lost wax casting method, a method of forming a ceramic material on a refractory cast and then baking the formed ceramic material using a vacuum electric furnace to fabricate a prosthesis, or a like.
However, to fabricate a dental prosthesis by using the lost wax casing method or the baking method as described, many procedures to be performed manually by a dental technician are required. These procedures present a problem in that they are exact and complicated work, as a result, requiring a lot of process and time. Also, quality of a dental prosthesis varies depending on a degree of skill of a dental technician.
To solve these problems, in recent years, a dental CAD/CAM (Computer Aided Design and Computer Aided Manufacturing) system has been developed in which three-dimensional shape data on a dental prosthesis is created and, based on the three-dimensional data, a dental prosthesis is fabricated by using a machine such as a milling machine, which makes it possible to fabricate a stable-quality dental prosthesis.
In the CAD/CAM, it is important how determine a margin line between an abutment tooth and a dental prosthesis.
When a margin line is set, as a preparatory step, a plaster model containing an abutment tooth to which a dental prosthesis is applied is fabricated. Next, a plaster model is fabricated with its margin portion made clear, to be used for three-dimensional shape measurement. That is, in many cases, a margin portion exists within a gingiva and, therefore, by deleting a dispensable portion corresponding to the gingiva from the plaster model, a model having a clear margin portion to be used for the three-dimensional shape measurement is made. Then, by obtaining three-dimensional shape data from the plaster model, and a margin line is detected from the obtained three dimensional shape data. As methods for detecting and setting a margin line, a method of applying a maximum contour portion as a margin or a method of using a maximum point of inflection on an external contour line as a margin line [see, for example, Patent Reference 1 (Japanese Patent Application Laid-open No. 1993-269146)], or a method of using a shadow produced by illuminating a tooth as a margin line [see, for example, Patent Reference 2 (Japanese Patent Application Laid-open No. 2000-185060)] are known.
In the margin line setting process described above, since a margin line is determined uniformly from the three-dimensional data, if a dental technician fails to form an abutment tooth having a suitable shape or if a dental technician deletes erroneously an appropriate portion when fabricating a model, there is a fear of a failure in properly setting a margin line.
To solve this problem, technology by which an operator of a CAD system can freely set a margin line is known [see, for example, Patent Reference No. 3 (Japanese Patent NO. 3460741). According to this technology, a longitudinal cross-sectional diagram of an original model body of a tooth or a like is displayed on a screen and a margin portion is determined by an operator on the longitudinal cross-sectional diagram and then a plurality of the longitudinal cross-sectional diagrams of a plurality of original model bodies is displayed for the specification of the margin portions and respective margin portions are connected so as to be joined to set a margin line.
However, the above-described technology by which an operator of a CAD system can freely set a margin line has a problem. That is, it is necessary that the procedures in which the operator sets an appropriate margin portion while watching each cross-sectional diagram are repeated a plurality of times (for example, 36 times), which requires a lot of work and time of the operator. Moreover, when a margin portion is to be set on each cross-sectional diagram, accurate indication of a margin portion by using an input device such as a mouse is necessary, which requires delicate and exact work and skill of an operator, as a result, imposing a load on the operator.